A HOMOGENEOUS MODEL OF UPPER LAYER CIRCULATION IN INDO-PACIFIC REGION

A homogeneous model is proposed to study the upper layer circulation in the Indo-Pacific region,the sources of the Indonesian throughflow (TF) and the North Equatorial Countercurrent (NECC), and the relations of the the with the North Equatorial Current (NEC) and the South Equatorial Current (SEC). The results revealed that the upper layer circulaton, as part of the Pacific Ocean general circulation, is mainly controlled by geostrophic balance; that the NECC’s volume transport is mainly sup plied by the NEC, and its variation has closer relation to the NEC than the SEC; that the TF, whose volume transport is jointly supplied by the NEC through the Mindanao Current (MC) and the SEC, with the NEC being the first source, has significant influence on the circulation structure; and that a large Celebes Sea cyclonic circulation not mentioned elsewhere so far, exists in the calculated results.

Early divergence and differential population histories of the Indo-Pacific humpback dolphin in the Pacific and Indian Oceans

The currently recognized Indo-Pacific humpback dolphin occurs in estuaries and surrounding shallow waters from the South China Sea to the Asian coast of the Indian Ocean.However,a recent study suggested that the humpback dolphin from the Bay of Bengal may represent a distinct phylogenetic species.In this study,we sequenced 915-bp mtDNA segments from five geographic populations in both Chinese and Thai waters;together with previously published sequences,these data revealed that the ancestral Indo-Pacific humpback dolphin might have split during the transition from the Oligocene to Miocene(23.45 Mya,95%HPD:16.65–26.55 Mya),and then dispersed along the Pacific and Indian Ocean coasts of Asia.Genetic differentiation was detected between most of the examined populations,except for only a few pairwise populations in the northern South China Sea.Genetic differentiation/distance between the humpback dolphins from the northern and southern South China Sea met the sub-species threshold value proposed for marine mammals,whereas that between the humpback dolphins in the Pacific and the Indian Ocean was above the species threshold.Bayesian inference of historic gene flow indicated low but constant northward gene flow along the Indian Ocean coast;however,there was a recent abrupt increase in gene flow in the Pacific region,likely due to the shortening coastline at the low stand of sea level.Our results revealed that the current taxonomic classification of Indo-Pacific humpback dolphins may not reflect their phylogeography.

Novel insights into the spatial genetic patterns of the finless porpoise from East to Southeast Asia

Several cetacean species are endemically distributed throughout the Indo-Pacific.Due to disproportionate sampling and research efforts across the Indo-Pacific region,the spatial genetic structure of these species remains poorly understood.This has led to poor phylogeographic knowledge and ambiguous taxonomic classification of many Indo-Pacific cetacean species.Of these,the finless porpoise(genus Neophocaena)is a small cetacean obligatory to the inshore waters from East Asia to the Persian Gulf of the Indian Ocean.To date,two species are generally recognized:the narrow-ridged finless porpoise inhabiting temperate and subtropical waters,and wideridged finless porpoises inhabiting subtropical and tropical waters.Early research efforts focused on the temperate waters off the northern China.However,recent studies have proposed that the primary divergence within the genus may lie between the Indian Ocean and Pacific region,which remains to be tested with more samples from tropical and subtropical regions.Here,we examined the genetic relationship among the finless porpoises from the Gulf of Thailand to the Taiwan Strait using both mitochondrial and autosomal markers.Bayesian assignment analysis suggested a minimum of four genetic populations within the study areas,corresponding to the narrowridged finless porpoise from the Taiwan Strait(TWSn),and the three wide-ridged finless porpoise populations from the Taiwan Strait(TWSw),Pearl River Delta region(PRDw),and the Gulf of Thailand(Thaiw),respectively.The minimum spanning network of the mtDNA control region found shared haplotypes among finless porpoises in Chinese waters,but those from the Gulf of Thailand formed a unique matriline lineage.Consistently,the genetic differentiation or divergence within the South China Sea(Thaiw vs.PRDw)appears to be higher than that of most finless porpoise populations examined to date,and meets the threshold values of species or sub-species level proposed for the cetacean species.The Mantel test detected a strong correlation between the geographic and genetic matrices within the South China Sea(r>0.99,p<0.001),indicating that the divergence associated with isolation-by-distance(IBD)has been accumulating in recent history.Our results imply that the formation and maintenance of the spatial genetic pattern of the finless porpoise is more complex than previously thought.However,this cannot be addressed by the current taxonomic classification of the genus.